Move the contents of a vector. The two vectors must have the same
length.

If the vectors do not overlap, then this is equivalent to copy.
Otherwise, the copying is performed as if the source vector were
copied to a temporary vector and then the temporary vector was copied
to the target vector.

Move the contents of a vector. The two vectors must have the same
length, but this is not checked.

If the vectors do not overlap, then this is equivalent to unsafeCopy.
Otherwise, the copying is performed as if the source vector were
copied to a temporary vector and then the temporary vector was copied
to the target vector.